Each of the muscles in the lower leg are contained in what is called a muscle compartment. Just like an orange or grapefruit, where the fruit is divided by fibrous sheaths into identifiable sections, the muscles of the lower leg are also divided by fibrous sheaths into identifiable muscle compartments. There are four muscle compartments in the lower leg: two in the back of the lower leg (i.e. posterior compartments), one on the front of the lower leg (i.e. anterior compartment) and one on the outside of the lower leg (i.e. lateral compartment). Each of the four muscle compartments contain at least two individual muscles, which are surrounded by the fibrous sheath which wraps around the muscles of the compartment.
Because of the arrangement of the muscles of the lower leg into four compartments, an individual can develop two types of compartment syndrome: acute and chronic. Acute compartment syndrome is caused by direct trauma to the lower leg, such as that occurs during a motor vehicle accident where possibly one of the leg bones is broken. Blood rushing into the muscle compartment has no way to escape, causing a relatively sudden rise in the pressure in the muscle compartment. The increased pressure inside the muscle compartment can become so high that it clamps down on the arteries and nerves going through the leg into the foot. The result may be a loss of pulse and blood supply to the foot, loss of nerve function to the foot, and severe pain. Acute compartment syndrome requires immediate surgical attention or the individual may develop permanent deformity and disability in the leg and foot.
The more common form of compartment syndrome is seen in athletes who exercise heavily and is called chronic exertional compartment syndrome (CECS). CECS is caused by the increase in pressure in the muscle compartment, which results from the muscles actually expanding in volume because of the increased blood flow to the muscles during exercise. If the sheath or compartment wall is particularly tight and thick, then as the athlete's muscles become larger over time from exercise the muscle compartment will become tighter. The compartment at the front of the leg is the most common muscle compartment to be affected by CECS and the pain that results is thought by many athletes to be shin splints. For runners, pain from CECS will generally occur within 20-40 minutes into a run and the pain may become so severe that continuing exercise past that point is impossible.
A thorough history and physical examination must be made of the individual with suspected chronic exertional compartment syndrome. The podiatrist will be most interested as to the time during exercise that the pain starts in the leg, where the pain is located, and whether the pain dissipates somewhat with rest. The symptoms from CECS generally starts at the same time or at the same mile mark during running and also usually gets better soon after as the individual stops exercising.
During the physical examination, the podiatrist will inspect the leg to determine which muscle compartment is affected and try to rule out any other pathology in the same area such as stress fractures, muscle strain, tendinitis, or shin splints. Additional tests such as x-rays, bone scans or MRI scans may be ordered depending on the most likely cause of the pain. Even though the podiatric physician can diagnose CECS relatively confidently by taking the proper history and physical of the patient, the only certain way to diagnosis the condition it is to have the muscle compartmental pressure measured at rest, during exercise and after exercise. Most doctor's offices do not have the special instrumentation to make this diagnosis and often the patient must be sent to a large hospital or sports clinic to have the test performed.
Chronic exertional compartment syndrome may be treated conservatively by modifying the type, duration and frequency of the sports activity that causes the pain. The condition is often successfully treated by altering the surfaces the individual runs on and the shoes they run in. In addition, CECS sometimes responds to altering the function of the muscles of the lower leg with in-shoe custom supports such as functional foot orthotics. If all conservative measures do not resolve the pain from CECS adequately, the podiatrist may refer the patient to an orthopedic surgeon for possible surgical release of the sheath surrounding the muscle compartment. In general, most patients who have surgical release of the muscle compartment sheath are able to resume unrestricted exercise within a few months of the procedure. Many notable athletes have had the compartment release surgical procedure performed and have returned to training without pain or limitations.